1. Field of the Invention
The present invention relates to a method for producing an R-T-B-M sintered magnet from R-T-B-M raw materials where R is at least one element selected from rare earth elements including Sc and Y, wherein T is at least one element selected from Fe and Co, wherein B is boron, and wherein M is at least one element selected from Ti, Ni, Nb, Al, V, Mn, Sn, Ca, Mg, Pb, Sb, Zn, Si, Zr, Cr, Cu, Ga, Mo, W, and Ta.
2. Description of the Prior Art
Since the discovery of the sintered Nd—Fe—B permanent magnet by Mr. Sagawa and others in 1983, its fields of application have been continuously expanding. Currently, the fields of application include initial medical magnetic resonance imaging (MRI), voice coil motors (VCM) for hard disk drives, CD Pickup Mechanisms, other medical, and information technologies. The application is also gradually expanding to include fields of energy conservation and environmental protection such as new energy vehicles, generators, wind generators, air conditioning and refrigerator compressors, and lift motors.
Due to increased use of the sintered Nd—Fe—B permanent magnetic materials, rare earth material resources have become scarce. Accordingly, decreasing the usage amount of the rare earth element, especially the heavy rare earth element, has become very important. Such rare earth magnet can be produced by a method as set forth in the Chinese Patent Application ZL01116130.5, published as CN1323045A. The method disclosed in the Chinese Patent Application includes a first step of casting the R-T-B-M raw materials into an alloy sheet. Next, the alloy sheet is subjected to a hydrogen atmosphere in a hydrogen decrepitation process at an absorption pressure to expand and break-up the alloy sheet into powder. The hydrogen is degassed from the hydrogen atmosphere. The next step of the method is injecting the powders into a mill in a stream of inert gas. The powders in the inert gas are milled to produce a mixture of particles. Next, the particles are mixed with a lubricant. After mixing with the lubricant, the particles are molded into a block. The block is subjected to isostatic pressure to the block to increase the density of the block. The block is then heated at a predetermined sintering temperature to further densify the block. After heating the block, the block is aged at a cooler temperature than the predetermined sintering temperature and over a predetermined time to harden the block.